The scope of this study is fully embedded within the ANDRILL (ANtarctic geological DRILLing) Project objectives to improve understanding of Antarctica's role in Cenozoic global climatic changes. Despite the key role that Antarctica plays in today's climate, our understanding of this continent is still at its infancy with respect to other areas of the globe. Particularly debated is the middle and late Miocene when the continent underwent a significant climate change from a climatic optimum (MMCO) to a glacial phase. Diatom biostratigraphy has played a key role so far in reconstructing Antarctic climate history. The contribution of this research to this discipline is addressed in three separate manuscripts, mainly articulated as chronostratigraphic and taxonomic improvements within the latest early to middle Miocene.
Study of the newly collected AND-1B and AND-2A drillcores in the McMurdo Sound area allow the identification of additional Denticulopsis species as key biostratigraphic markers for the middle Miocene to Pliocene ( D. ichikawae and D. okunoi first and last occurrences, D. delicata first occurrence) with the clear potential of improve resolution of future age models.
Refined analysis of the middle Miocene diatom assemblage in the AND-2A drillcore (230.25-434.35 mbsf) identifies several useful biostratigraphic datums ( Denticulopsis maccollumii, Denticulopsis lauta, Actinocyclus ingens, Nitzschia sp . 17, Actinocyclus ingens nodus ) and indicates open water conditions in the McMurdo Sound area. This record is then correlated across the Ross Sea with the herein revised diatom biostratigraphy of existing Deep Sea Drilling Project drillcores embedding middle to late Miocene sequences (DSDP 272, 273 and 274). A key biostratigraphic framework from D. maccollumii FAD to D. simonsenii FAD is produced for future reference.
Additionally, this study explores probabilistic assessments of the biochronological dataset for the Late Neogene Southern Ocean via RASC (Ranking and Scaling), comparing the results with the CONOP (Constrained Optimization) deterministic approach. Main purpose is to independently assess the reliability of taxa and biostratigraphic events for correlation purposes. The stratigraphic fit obtained from the comparison of the two ordinal sequences is excellent. Both programs identify the same biostratigraphic events unsuitable for biostratigraphic purposes corroborating quantitative biostratigraphic methods as a powerful frontier in biostratigraphy.
